Measurement device for measuring the mass of a flowing medium

ABSTRACT

A measurement device for measuring the mass of a medium flowing along a flow direction, in particular the intake air mass of an internal combustion engine, has a plate-shaped sensor element, which is inserted into a recess of a sensor support. The sensor element includes a membrane that supports a measuring element, which membrane encloses a hollow space embodied in the sensor element on the side remote from the sensor support. The sensor element is secured in the recess by means of a glue between the sensor support and a bottom face of the sensor element oriented toward the sensor support. According to the invention, the glue constitutes a glue seam that extends around the hollow space of the sensor element between the sensor support and the bottom face of the sensor element and is only open on the side remote from the flow direction by means of at least one recess in order to ventilate the hollow space.

FIELD OF THE INVENTION

The invention is directed to improvements in a measurement device formeasuring the mass of a flowing medium.

BACKGROUND OF THE INVENTION

A measurement device has already been disclosed by German PatentPublication 195 24 634 A1, which includes a plate-shaped sensor elementwith a dielectric membrane that is inserted into a recess of a sensorsupport. The sensor element is made of a semiconductor material, e.g.silicon, and is manufactured in a micromechanical construction. Themembrane is comprised of a dielectric material, for example siliconnitride or silicon oxide. A measurement resistor and a heating resistorare disposed on the dielectric membrane, which are to a large extentthermally insulated from a silicon frame that encompasses the membranedue to the thin embodiment of the membrane and the low heat conductivityof the dielectric membrane. Between the dielectric membrane and thesensor support, there is a hollow space in the plate-shaped sensorelement, which extends from a bottom face adjoining the sensor supportto the dielectric membrane and is manufactured, for example, by means ofan etching process. The sensor element is fixed in the recess of thesensor support by means of a glue. Since the relatively thin membranemust be protected from excess pressure peaks, a ventilation of thehollow space provided underneath the membrane cannot be omitted. Theventilation of the recess in the measurement sensor or the rear of themembrane, however, must take place so that a flow of the medium is keptaway from the rear of the membrane in order to prevent the rear flowfrom contributing to the measurement signal. In order to prevent thepenetration of glue into the hollow space adjoining the membrane, thegluing region does not extend over the entire sensor element, but thesensor element is glued into the recess of the sensor support on onlyhalf of its surface and the region of the sensor element which has theelectric membrane is disposed freely in the recess. In order to preventunderflow of the membrane, i.e. a flow of the medium to the hollow spaceembodied underneath the membrane, or to at least counteract this, a flowconduit is provided, which is embodied in the sensor support as achannel-shaped recess and extends around the sensor element. At the sametime, the provision is made that the recess embodied in the sensorsupport is matched to the dimensions of the sensor element so that onlya small gap respectively remains between the lateral boundary of thesensor element and the lateral boundary of the recess in the sensorsupport, which permits only a throttled flow of the medium to the hollowspace disposed underneath the dielectric membrane.

However, it is disadvantageous in this embodiment that the sensorelement must be aligned with high precision in regard to the recess ofthe sensor support during mounting in order to produce the extremelynarrow gap. But this task cannot always be reliably fulfilled fortolerance reasons and due to manufacturing variations so that notinsignificant losses in efficiency occur during manufacture.

A measurement device can be inferred from German Patent Publication 4219 454 A1, in which a sensor element with a dielectric membrane isinserted into the recess of a cooling body. The cooling body has aventilation bore between the cooling ribs in order to assure theventilation of the rear of the membrane.

OBJECTS AND SUMMARY OF THE INVENTION

A principal object of the measurement device according to the inventionis to provide the advantage over the prior art that in themanufacturing, a relatively low tolerance must be maintained in thepositioning of the sensor element in relation to the recess of thesensor support. As a result, the manufacturing efficiency is increasedand the manufacturing costs are reduced. Furthermore, the manufacturingspeed can be increased. In another object of the invention theventilation of the rear of the membrane remote from the flowing mediumis reliably assured with a sufficient opening cross section so that adestruction of the sensor element due to pressure peaks is prevented.The glue seam is used simultaneously for tolerance compensation betweenthe sensor element and the sensor support as well as for compensation ofdifferent coefficients of thermal expansion.

Yet another object of the invention provides that the glue seam extendsinto a region beneath the connecting elements for connection to theconnecting wires or that an additional glue seam is provided in thisregion in order to assure a reliable fixing of the sensor element in thevicinity of the connecting elements and to counteract the danger ofbreakage when the connecting wire is attached, e.g. by means of bonding.

Still another object of the invention is to embody a recess in thesensor support, which communicates with the hollow chamber of the sensorelement and is not completely covered by the sensor element. This recessof the sensor support can, for example, be produced by means ofembossing. The recess of the sensor support reliably assures theventilation of the rear of the membrane.

Still a further object of the invention provides that on a support facedisposed opposite from the bottom face of the sensor element, spacerscan be provided, which are produced, for example, by means of embossing,which set the distance between the sensor support and the bottom face ofthe sensor element to a precisely defined dimension. Furthermore, it isadvantageous if the sensor support has at least one glue displacementchamber into which excess glue that is used to produce the glue seam canbe displaced upon insertion of the sensor element into the recess of thesensor support. In this manner, an accumulation of glue at unfavorablelocations is avoided, particularly in the hollow space of the sensorelement that is formed underneath the membrane. The mechanical stress ofthe sensor element is minimized through the use of an elastic siliconglue, even when there are differences in thermal expansion coefficientsbetween the material of the sensor element and the material of thesensor support.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are shown in simplified fashionin the drawings and will be explained in more detail in the descriptionthat follows.

FIG. 1 shows a section along the line I—I in FIG. 2, through ameasurement device corresponding to a first exemplary embodimentaccording to the invention,

FIG. 2 is a top view of the measurement device according to FIG. 1,

FIG. 3 is a top view of a measurement device corresponding to a secondexemplary embodiment according to the invention, and

FIG. 4 shows a section along the line IV—IV in FIG. 3.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The sensor support 1 depicted in a sectional view in FIG. 1 is providedfor a plate-shaped sensor element 2. The sensor support 1 and the sensorelement 2 are part of a measurement device not shown in detail, which isfor measuring the mass of a flowing medium, in particular the intake airmass of an internal combustion engine.

The sensor support 1 is used to contain and secure the sensor element 2,which has a membrane-shaped sensor region, which is embodied, forexample, in the form of a dielectric membrane 4. The sensor element 2 orthe membrane 4 can be produced by means of etching a semiconductor body,for example a silicon wafer, in a so-called micromechanicalconstruction, wherein a hollow space 5 is produced underneath themembrane 4. At least one temperature-dependent measurement resistor 6and for example at least one heating resistor that is not shown, whichare for example likewise produced by means of etching, are provided onthe membrane 4 in order to measure the mass of the flowing medium.Outside the membrane 4, a reference resistor can be provided on thesensor element 2. The measurement resistor 6, the heating resistor, andthe reference resistor are electrically connected to an electronicregulation circuit that is not shown in detail, for example by means ofconductor strips and by means of wires 10 that are attached toconnecting elements 28 which are embodied as bonding pads. Theelectronic regulation circuit is used in a known manner for supplyingpower or voltage to the resistors on the sensor element 2 and forevaluating the electrical signals emitted by the resistors. Theregulation circuit can be accommodated, for example, in a housing oroutside the housing of the measurement device.

The dielectric membrane 4 is comprised, for example, of silicon nitrideand/or silicon oxide. The heating resistor can be embodied in the formof an electrically resistive layer that heats up with the flow ofcurrent and heats the membrane 4 to a temperature that is higher thanthe temperature of the medium to be measured. The heating resistor can,for example, be comprised of a metal or also of a correspondingly dopedsilicon. The measurement resistor and the reference resistor can, forexample, be comprised of an electrically resistive layer whoseconductivity changes as a function of the temperature. Suitablematerials for these resistive layers are metals or correspondingly dopedsilicon.

The sensor element 2 has a plate-shaped, for example rectangular formand is aligned with its surface 8 oriented toward the flowing mediumapproximately parallel to the medium flowing into the plane of thedrawing in FIG. 1, wherein a short side of the, for example, rectangularsensor element 2 extends in the flow direction 9. The flow direction 9of the medium is indicated in FIG. 2 by means of corresponding arrowsand travels from top to bottom there. The heating resistor attached tothe membrane 4 heats the membrane 4 to a temperature that is higher thanthe temperature of the medium flowing past. The heat quantity of theheating resistor, which is dissipated from the medium flowing pastessentially due to convection, depends on the mass of the flowing mediumso that the mass of the flowing medium can be established by measuringthe temperature of the membrane 4. The measurement of the membranetemperature can be carried out by means of the measurement resistor 6 orby measuring the resistance of the heating resistor. The referenceresistor is used to compensate for the influence of the temperature ofthe medium flowing past.

The sensor support 1 is preferably comprised of metal and can bemanufactured by folding a thin metal strip, for which punching, bending,folding, embossing, and stamping processes are suited. In the finishedstate of the bent metal strip, for example two elements 14 and 15 thatare the same size rest against each other. In the following description,the element 14 that is not bent and encompasses the sensor element 2will be referred to as the frame element 14 and the element 15 bentunder it will be referred to as the securing element 15. In thecompletely bent state of approximately 180°, the securing element 15covers an opening 16 of the unbent frame element 14 in order, togetherwith the frame element 14, to define a recess 17 for containing thesensor element 2. The frame element 14 or the recess 17 has a crosssection which approximately corresponds to the for example rectangularshape of the sensor element 2. The sensor element 2 is accommodated inthe recess 17 with its surface 8 approximately flush to a surface 18 ofthe frame element 14.

Before the folding of the metal strip, the securing element 15 can bedeformed by means of a tool that engages the outer surface 22 of thesecuring element 15, for example a stamping tool, so that twoprojections 20, 21 are produced in the cross section in the exemplaryembodiment. In the cross section depicted in FIG. 1, the projections 20,21 are each adjoined by glue displacement chambers 23, 24, and 25 to bedescribed in more detail. As best shown in FIG. 2, on its end faceoriented toward the flow direction 9, the sensor support 1 has aflattened region 49 in order to improve the flow behavior and tocounteract the deposit of dirt particles.

According to the invention, the plate-shaped sensor element 2 is gluedinto the recess 17 of the sensor support 1 by means of a glue that isapplied along glue seams 26, 27 in the form of glue beads. As shown moreclearly in FIG. 2, which is a top view of the detail of the measurementdevice according to the invention, two glue seams 26 and 27 are providedin the exemplary embodiment depicted. A first glue seam 26 is embodiedas a cruciform shape in the exemplary embodiment shown in FIGS. 1 and 2and is used to glue the sensor element 2 onto the plateau-shapedprojection 20. Connecting elements 28 embodied as bonding pads areprovided on the surface 8 remote from the securing element 15 of thesensor support 1, in the vicinity of the plateau-shaped projection 20,and are used to electrically connect conductor strips of the sensorelement 2 to connecting lines 10. The first glue seam 26 is used to fixthe sensor element 2 in the vicinity of the connecting elements 28 inorder to produce a secure bonding connection.

As shown in FIG. 2, the second glue seam 27, however, is embodied asU-shaped in the exemplary embodiment shown in FIGS. 1 and 2. The secondglue seam 27 is used to glue the sensor element 2 in the vicinity of theplateau-shaped projection 21. The two glue seams 26 and 27 arerespectively embodied between the bottom face 29 of the sensor element 2and the surface 31 or 30 of the recesses 20 and 21 of the securingelement 15.

According to the invention, the second glue seam 27 is is embodied sothat it extends around the hollow space 5 between the sensor support 1and the bottom face 29 of the sensor element 2 and is only opened bymeans of a recess 40 on the end remote from the flow direction 9. In theexemplary embodiment shown in FIGS. 1 and 2, the U-shape glue seam has asection 41 oriented toward the flow direction 9 as well as two sections42 and 45 extending in the flow direction 9. The sections 42 and 45extending in the flow direction 9 constitute two legs of the U-shapedsecond glue seam 27. In the exemplary embodiment of FIGS. 1 and 2, therecess 40 extends between the two sections 42 and 45 that extend in theflow direction 9, i.e. the glue seam 27 is open over the entire regionremote from the flow direction 9. The recess 40 is used for theventilation of the hollow space 5 of the sensor element 2. Thisventilation is necessary since otherwise static pressure fluctuations inthe flowing medium to be measured, in particular excess pressure peaks,can lead to a destruction of the dielectric membrane 4. However, theflowing medium must be prevented from flowing along the rear 44 of themembrane 4 since this would lead to an undesirable contribution to themeasurement signal, which would lead to an indefinite andnon-reproducible measurement result. According to the invention,therefore, the proposal is made to route the glue seam 27 so that itextends around the hollow space 5 of the sensor element 2 and is openedby a corresponding recess 40 only on the side remote from the flowdirection 9.

The opening cross section of the recess 40 thereby defines a throttlelocation. This opening cross section is suitably established so that asufficiently rapid pressure compensation is produced between the frontof the membrane 4 oriented toward the flowing medium and the rear 44 ofthe membrane 4 oriented toward the hollow space 5 and away from theflowing medium, which pressure compensation prevents a destruction ofthe membrane 4. On the other hand, however, the opening cross section ofthe recess 40 must have small dimensions so that a flow of the medium inthe hollow space 5 is prevented or is at least sufficiently suppressed.The opening cross section of the recess 40 is determined on the one handby the width b of the recess 40 shown in FIG. 2 and is determined on theother hand by the thickness d of the glue seam 27 shown in FIG. 1. Thethickness of the glue seam d can be determined, for example, by spacers43 a-43 i. The spacers 43 a-43 i can be embodied, for example, by meansof a stamping process by a stamping tool embodied for example in theform of a needle which engages the securing element 15 on the outer face22. Alternatively, it is also conceivable to embody the spacers on thesensor element 2 by means of a suitable etching process or to dispersethe spacers in the glue that constitutes the glue seams 26 and 27, e.g.as fine pellets with a constant diameter.

The glue seams 26 and 27 can be applied as fine glue beads with aconventional metering process. A glue that remains elastic afterhardening is preferably suitable for use as the glue, in particular anelastic silicon glue. Mechanical stresses between the sensor element 2and the sensor support 1 are therefore minimized. Mechanical stressesoccur particularly as a result of the different thermal expansioncoefficients of the sensor support 1 that is preferably made of a sheetmetal and the sensor element 2 that is preferably made of asemiconductor material. With the use of the measurement device accordingto the invention to measure the intake air mass of an internalcombustion engine, the intake air to be measured can be subjected toconsiderable temperature fluctuations depending on the externaltemperature of the vehicle.

On the side oriented toward the flow direction 9, the glue displacementchambers 23, 24, and 25 described above are connected by means of otherglue displacement chambers 46 and 47. In the exemplary embodiment shownin FIGS. 1 and 2, the glue displacement chambers 23 and 24 are alsoconnected by means of another glue displacement chamber 48 remote fromthe flow direction 9. When the sensor element 2 and the sensor support 1are assembled, excess glue applied can escape into the glue displacementchambers 23, 24, 25, 46, 47, 48, as schematically depicted in FIG. 1. Asa result, when the sensor element 2 and the sensor support 1 areassembled, glue is in particular prevented from penetrating into thehollow space 5 or even reaching the rear 44 of the membrane 4. The glueseam 27 must be placed so that a penetration of the glue into the hollowspace 5 is reliably prevented since this can considerably impair thefunctional performance of the measurement device according to theinvention.

A second exemplary embodiment of the measurement device according to theinvention is depicted in FIGS. 3 and 4. While FIG. 3 shows a top view ofthe measurement device according to the invention, FIG. 4 shows asection along the line IV—IV in FIG. 3. Elements already described aboveare indicated with corresponding reference numerals so that a repeatdescription is not necessary in this regard.

The difference in relation to the exemplary embodiments alreadydescribed in relation to FIGS. 1 and 2 is comprised on the one hand inthat a glue seam 60 that is embodied in one piece, extends in a G-shapearound the hollow space 5 of the sensor element 2. The glue seam 60 hasa section 61 oriented toward the flow direction 9, two sections 62 and63 extending in the flow direction 9, and a section 64 remote from theflow direction 9. The section 64 remote from the flow direction 9 doesnot completely connect the sections 62 and 63 extending in the flowdirection 9 so that a recess 40 is produced on the side remote from theflow direction 9. In the exemplary embodiment depicted in FIG. 3, therecess 40 extends from a first section 62 running in the flow direction9 to a free end 65 of the section 64 of the glue seam 60 remote from theflow direction 9.

However, embodiments are also conceivable in which the recess 40interrupts the section 64 remote from the flow direction 9 at anotherpoint. Also, a number of such recesses can be provided in the-section 64remote from the flow direction 9. The second section 63 running in theflow direction extends so that it reaches into the region beneath theconnecting elements 28 that are embodied in the form of bonding pads sothat the sensor element is under-supplied with glue in the vicinity ofthe connecting elements 28. As a result, a high breaking strength of thesensor element 2 is assured during the application of the bondingconnections. Furthermore, the sensor element 2 in the region of theconnecting elements 28 is fixed particularly well by means of the glueseam 60 so that a good bonding connection can be produced even with theuse of an elastic glue, e.g. a silicon glue.

In the exemplary embodiment shown in FIGS. 3 and 4, the glue seam 60 canreach into the edge region of the recess 17 embodied in the frameelement 14. When the sensor element 2 is assembled with the sensorsupport 1, in order to prevent glue from penetrating into the hollowspace 5 of the sensor element 2 or even reaching the membrane 4, arecess 66 is provided in the securing element 15 of the sensor support1, e.g. by means of an embossing process. The recess 66 is used as aglue displacement chamber and absorbs excess glue. At the same time, therecess 66 is also used to ventilate the hollow space 5 of the sensorelement 2. As can be seen from FIG. 3, the recess 66 is embodied assubstantially L-shaped and extends through the recess 40 of the glueseam 60 until it reaches an elongated section 67. The elongated section67 is therefore not covered by the sensor element 2 and is connected tothe flowing medium to be measured for the pressure compensation, e.g. byway of bores, not shown, in the securing element 15.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A measurement device for measuring an intake airmass along a flow direction (9) of an internal combustion engine,comprising a plate-shaped sensor element (2), which is inserted into arecess (17) of a sensor support (1) and has a membrane (4) that supportsa measuring element (6), which membrane encloses a hollow space (5)embodied in the sensor element (2) on a side remote from the sensorsupport (1), wherein the sensor element (2) is secured in the recess(17) by a glue means provided between the sensor support (1) and abottom face (29) of the sensor element (2) oriented toward the sensorsupport (1), the glue means having a glue seam (27; 60) that extendsaround the hollow space (5) of the sensor element (2) between the sensorsupport (1) and the bottom face (29) of the sensor element (2), saidglue means being open only on a side remote from the flow direction (9)by means of at least one recess (40) in order to ventilate the hollowspace (5).
 2. The measurement device according to claim 1, furthercomprising the glue seam (27) extends in a substantially U-shape aroundthe hollow space (5) and is provided with a section (41) oriented towardthe flow direction (9) and two sections (42, 45) extending in the flowdirection (9).
 3. The measurement device according to claim 1, furthercomprising the glue seam (60) extends in a substantially G-shape aroundthe hollow space (5) and said glue seam (60) comprises a first section(61) oriented toward the flow direction (9), second and third sections(62, 63) extending in the flow direction (9), and a fourth section (64)remote from the flow direction (9), and the fourth section (64) remotefrom the flow direction (9) does not completely connect the second andthird sections (62, 63) extending in the flow direction (9).
 4. Themeasurement device according to claim 1, further comprising theplate-shaped sensor element (2) is provided with connecting elements(28) on a surface (8) remote from the sensor support (1), for connectionto connecting wires (10) and another glue seam (26) is provided in aregion opposite from the connecting elements (28), between the sensorsupport (1) and the bottom face (29) of the sensor element.
 5. Themeasurement device according to claim 2, further comprising theplate-shaped sensor element (2) is provided with connecting elements(28) on a surface (8) remote from the sensor support (1), for connectionto connecting wires (10) and another glue seam (26) is provided in aregion opposite from the connecting elements (28), between the sensorsupport (1) and the bottom face (29) of the sensor element.
 6. Themeasurement device according to claim 3, further comprising theplate-shaped sensor element (2) is provided with connecting elements(28) on a surface (8) remote from the sensor support (1), for connectionto connecting wires (10) and another glue seam (26) is provided in aregion opposite from the connecting elements (28), between the sensorsupport (1) and the bottom face (29) of the sensor element.
 7. Themeasurement device according to claim 4, further comprising the otherglue seam (26) has a substantially cruciform shape.
 8. The measurementdevice according to claim 5, further comprising the other glue seam (26)has a substantially cruciform shape.
 9. The measurement device accordingto claim 6, further comprising the other glue seam (26) has asubstantially cruciform shape.
 10. The measurement device according toclaim 1, further comprising the plate-shaped sensor element (2) hasconnecting elements (28) on a surface (8) remote from the sensor support(1), for connection to connecting wires (10), the glue seam (27) isdisposed on three sides around the hollow space (5) extending betweenthe sensor support (1) and the bottom face (29) of the sensor element(2) and a region void of glue seam is disposed opposite from theconnecting elements (28).
 11. The measurement device according to claim2, further comprising the plate shaped sensor element (2) has connectingelements (28) on a surface (8) remote from the sensor support (1), forconnection to connecting wires (10), the glue seam (27) is disposed onthree sides around the hollow space (5) extending between the sensorsupport (1) and the bottom face (29) of the sensor element (2) and aregion void of glue seam is disposed opposite from the connectingelements (28).
 12. The measurement device according to claim 3, furthercomprising the plate-shaped sensor element (2) has connecting elements(28) on a surface (8) remote from the sensor support (1), for connectionto connecting wires (10), the glue seam (27) is disposed on three sidesaround the hollow space (5) extending between the sensor support (1) andthe bottom face (29) of the sensor element (2) and a region void of glueseam is disposed opposite from the connecting elements (28).
 13. Themeasurement device according to claim 1, further comprising a recess(66) is embodied in the sensor support (1), which communicates with thehollow space (5) of the sensor element (2) and is not completely coveredby the sensor element (2).
 14. The measurement device according to claim3, further comprising a recess (66) is embodied in the sensor support(1), which communicates with the hollow space (5) of the sensor element(2) and is not completely covered by the sensor element (2).
 15. Themeasurement device according to claim 10, further comprising a recess(66) is embodied in the sensor support (1), which communicates with thehollow space (5) of the sensor element (2) and is not completely coveredby the sensor element (2).
 16. The measurement device according to claim1, further comprising the sensor support (1) has at least one gluedisplacement chamber (23, 24, 25, 46, 47, 48; 66) disposed opposite thebottom face (29) of the sensor element (2) into which excess glue usedto form the glue seam (26, 27; 60) can be displaced upon insertion ofthe sensor element (2) into the recess (17) of the sensor support (1).17. The measurement device according to claim 2, further comprising thesensor support (1) has at least one glue displacement chamber (23, 24,25, 46, 47, 48; 66) disposed opposite the bottom face (29) of the sensorelement (2) into which excess glue used to form the glue seam (26, 27;60) can be displaced upon insertion of the sensor element (2) into therecess (17) of the sensor support (1).
 18. The measurement deviceaccording to claim 3, further comprising the sensor support (1) has atleast one glue displacement chamber (23, 24, 25, 46, 47, 48; 66)disposed opposite the bottom face (29) of the sensor element (2) intowhich excess glue used to form the glue seam (26, 27; 60) can bedisplaced upon insertion of the sensor element (2) into the recess (17)of the sensor support (1).
 19. The measurement device according to claim1, further comprising the glue means comprises an elastic silicon glue.20. The measurement device according to claim 1, further comprisingraised spacers (43 a-43 i) are provided on at least one of the supportfaces (30, 31) of the sensor support (1) opposite from the bottom face(29), which spacers determine a distance between the sensor support (1)and the bottom face (29) of the sensor element (2).